<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- `background: radial-gradient((shape? size? (at position?))?, start-color, ..., last-color)` ? 表示可省略 -->
    <style>
        .box{
            width:200px ;
            height: 200px;
            /* background-image: radial-gradient(circle at center , red,green,blue); */
            background-image: radial-gradient(circle at 10% 30% , red,green,blue);

        }
    </style>
</head>
<body>
    <div class="box">

    </div>
</body>
</html>